Recently an interesting paper was published on the economic motivation for raising coastal flood defences in Europe [1]. The authors find that at least 83% of flood damages in Europe could be avoided by elevating dykes in an economically efficient way along 23.7%-32.1% of Europe’s coastline. It would be interesting to have a similar look at the outcome if we add nature-based solutions to the equation.
The authors have built a probabilistic model to determine Cost Benefit Ratios for raising coastal flood defences under two sea level rise scenario’s. The Extreme Sea level in a 100 year event is expected to rise 34-76 cm under moderate emissions scenario’s (IPPC’s RCP4.5 scenario) and 58-176 cm under extreme emissions scenario’s (IPCC’s RCP8.5 scenario).
Let’s take a look at what the model predicts for the moderate emissions scenario (which at this moment in time is the more probable scenario). If we do nothing direct damages in Europe will increase from EUR 1.4 billion per year now, to EUR 209.8 billion per year in 2100. The authors have analysed what the costs and benefits would be when we adjust our coastal defences to cope with this rather enormous increase.
Their finding that at least 83% of the damages can be avoided by elevating dykes in an economically efficient way along 24-32% of the European coastline is quite a spectacular result. But why do the authors not conclude that it is possible to reduce the complete effect? That is because the authors took as a starting point that raising the dykes should be economically feasible. In large parts of Europe’s coastal areas that is not the case. Reasons for this are the characteristics of the coast (e.g. steep morphology) and the economic values to be protected. It was found that raising coastal protection was economically justified in areas where the population density exceeds 500 people/km2. This means mostly in urbanised areas.
We can safely conclude that adaptation has substantial economic benefits.
The authors have, for their European-wide model, assumed that raising coastal protection means constructing higher dykes. They point out in their paper that there are many other possible means to increase coastal safety, not in the least through nature-based solutions. Local studies can lead to all kind of tailor-made optimizations combining hard structures with nature-based solutions or other adaptation measures such as retreat or accommodate.
What this paper learns us in my opinion is that adaptation to sea-level rise is a sensible thing to do. It leads to significant economic benefits in terms of avoided damage and from the paper it can be derived that the total investment is feasible. It would be interesting to see how nature-based solutions will influence the outcome of this analysis. Nature-based solutions often require less investment than hard structures and produce additional benefits for society. This may lead to the conclusion that more reduction in damages is achievable with greater benefits.at lower cost.
Building on this paper, to develop an idea of where and which nature-based solutions can be applied, will show us an even more attractive path to navigate through the challenges associated with coming sea level rise. I am looking forward to the next paper addressing this.
[1] Economic motivation for raising flood defences in Europe, Vousdoukas, Mentaschi, Hinckel, Ward, Mongelli, Ciscar and Feyen, Nature Communications 2020 https://www.nature.com/articles/s41467-020-15665-3
